There are a number of procedures and applications that involve the formation of a temporary seal, coating or plug while other steps or processes are performed, where the seal, coating or plug must be later removed. Often such seals or plugs are provided to temporarily inhibit or block a flow pathway or the movement of fluids or other materials, such as flowable particulates, in a particular direction for a short period of time, when later movement or flow is desirable.
A variety of applications and procedures where temporary coatings or plugs are employed are involved in the recovery of hydrocarbons from subterranean formations where operations must be conducted at remote locations, namely deep within the earth, where equipment and materials can only be manipulated at a distance. One particular such operation concerns perforating and/or well completion operations incorporating filter cakes and the like as temporary coatings.
Perforating a well involves a special gun that shoots several relatively small holes in the casing. The holes are formed in the side of the casing opposite the producing zone. These communication tunnels or perforations pierce the casing or liner and the cement around the casing or liner. The perforations go through the casing and the cement and a short distance into the producing formation. Formations fluids, which include oil and gas, flow through these perforations and into the well.
The characteristics and placement of the communication paths (perforations) can have significant influence on the productivity of the well. Therefore, a robust design and execution process should be followed to ensure efficient creation of the appropriate number, size and orientation of perforations. A perforating gun assembly with the appropriate configuration of shaped explosive charges and the means to verify or correlate the correct perforating depth can be deployed on wireline, tubing or coiled tubing.
It would be desirable if the communication paths of the perforations could be temporarily blocked, filled or plugged while other operations are conducted that would cause problems if the perforations were left open. Such problems include, but are not necessarily limited to, undesirable leak-off of the working fluid into the formation, and possible damage to the formation.
The filter cake that is often deposited temporarily on the wellbore wall has been conventionally formed by using hydratable polymers, such as polysaccharides which increase the viscosity of the fluid, and/or other particles that filter out against the pores of the formation. However, a common problem with using polymer-based gelled fluids is that upon removal from the wellbore face damage occurs to the pores of the formation and permeability is reduced, which in turn compromises the wells' ability to flow hydrocarbons.
It would be desirable if the communication paths of the perforations could be temporarily blocked, filled or plugged while other operations are conducted that did not risk damage to the formation, or that greatly reduced any damage that does occur.